This application relates to a system and method for monitoring the quality of amniotic fluid during labor.
In recent years, it has become accepted that there is a need for more information concerning the condition within the uterus just prior to and during labour in order to predict and avoid birth complications. U.K. Patent Application No. 87 23605 (Publication No. 2195897) describes an intrauterine probe which enables certain conditions, especially the fetal heart rate and the intrauterine pressure to be continuously monitored during labor. Any monitoring system should desirably be non-invasive to the fetus and be capable of a continuous collection of data concerning the condition of interest.
During intrauterine life, the human fetus collects within its bowel a collection of debris known as meconium. Passage of meconium in utero occurs in about 10% of babies overall, probably as part of a sympathetic `fright, flight or fight` reaction. Because regular uterine contractions interfere with maternal blood flow within the placenta, the mean oxygen tension in fetal blood during labour drops from about 5 to 3 kPa. This is thought to be the major stimulus causing the fetus to pass meconium in utero; it occurs with increasing frequency as gestation advances, reaching almost one third of all fetuses by 42 weeks gestation.
In 90% of fetuses who pass meconium into the amniotic fluid there are no harmful effects. However, in about 10% of cases the fetus gasps, inhaling the sticky, particulate meconium into the upper respiratory tract. Once the baby is born, this particulate matter produces partial airways obstruction, leading to inability to inflate alveoli in some areas, and hyperinflation in others. This disease is known as meconium aspiration syndrome (MAS).
Attempts have been made to prevent MAS by careful suctioning of the baby's pharynx immediately after the head is delivered; unfortunately such measures are largely ineffective.
It appears that there is, as yet, no known effective prevention of this crippling and disabling condition. The main factor preventing progress is that the appearance of meconium into the amniotic fluid often remains undetected because the tight fit of the head in the pelvis does not allow amniotic fluid to drain out and become visible to the attending obstetrician.
There is therefore a need for a method of reliably monitoring the onset of meconium passage into the amniotic fluid and particularly one which can be carried out non-invasively to the fetus and continuously throughout labor.